Mass Flow Controller Thermal Sensor Gradient Cancellation

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Solution Overview

Problem

Mass flow controllers (MFCs) face challenges in accurately measuring fluid flow rates due to external thermal sources causing longitudinal and orthogonal thermal gradients, which can lead to incorrect flow rate readings.

Innovation Solution

A mass flow controller thermal sensor configuration featuring a capillary flow tube with upstream and downstream tube portions of equal lengths, arranged in a specific geometry to cancel the effects of longitudinal and orthogonal thermal gradients, utilizing a bridge circuit with differential amplification to generate a flow rate signal unaffected by these gradients.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a simple thermal sensor configuration is used, then device complexity is reduced, but measurement precision deteriorates due to thermal gradient interference

Engineering Contradiction:

Improvesensor configurationVSAvoidflow rate reading accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The thermal sensor is divided into multiple sensing elements (first upstream, second upstream, first downstream, second downstream) arranged in pairs along the capillary tube. Each element independently measures temperature at its location, and the differential amplifier compares temperatures between upstream and downstream elements to calculate flow rate while canceling thermal gradient effects.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The differential amplifier acts as an intermediary that processes temperature signals from multiple sensing elements. It calculates temperature differences between upstream and downstream elements, effectively eliminating the influence of thermal gradients and producing an accurate flow rate signal.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Length of moving object

If thermal sensing elements are placed close together, then device length is reduced, but measurement precision deteriorates due to increased thermal gradient effects

Engineering Contradiction:

Improvesensor lengthVSAvoidflow rate measurement accuracy

Core Design Contradiction:

Length of moving objectVSMeasurement precision

Solution Approach 1:

The sensing elements are positioned asymmetrically within the capillary tube structure, with specific spacing between upstream and downstream elements. This asymmetric arrangement, combined with differential measurement, allows the sensor to be compact while maintaining accuracy by canceling thermal gradient effects through the bridge circuit configuration.

Inventive Principle:

Principle #4Asymmetry

3Measurement precision

If multiple thermal sensing elements are used to cancel thermal gradients, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improveflow rate reading accuracyVSAvoidsensor configuration

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

Multiple thermal sensing elements are merged into a single integrated sensor assembly within the capillary tube. The upstream and downstream elements are positioned along the tube, and their signals are combined through the differential amplifier to produce a flow rate measurement that automatically compensates for thermal gradients.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The thermal gradients, which are harmful to measurement accuracy, are converted into a benefit through the differential measurement approach. By measuring temperature differences between upstream and downstream elements and using the bridge circuit, the thermal gradient effects cancel out, leaving only the flow-induced temperature changes that provide accurate flow rate information.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution effectively minimizes the impact of thermal gradients on flow rate measurements, ensuring accurate fluid flow rate determination and control, thereby maintaining precise flow control.

Implementation Method 1

a first pair of thermal sensing elements, adapted to output at least one signal comprising a sensing element voltage, coupled to the upstream tube portion

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

seeking to cancel the effects of longitudinal thermal gradients produced by external thermal sources acting on the upstream and downstream tube portions

Methodology Applied

Scientific EffectThermal gradient: Temperature Gradient

Implementation Method 3

a differential amplifier connected to the left and right node

Methodology Applied

Scientific EffectDifferential amplification:

Implementation Method 4

the sensing elements being configured to form a bridge circuit, the bridge circuit being arranged as part of a mass flow controller for voltage cancellation

Methodology Applied

Scientific EffectBridge circuit: Wheatstone Bridge

Data Source

PatentEP2338036B1Mass flow controller and method of operating the same

Publication Date: 2017.03.01 PROTERIAL LTD

AI summary

One embodiment of the present invention involves a thermal sensor and a method of using the same. One thermal sensor is adapted to output a signal which is unaffected by external longitudinal and orthogonal thermal gradients. In one embodiment, the mass flow controller thermal sensor comprises a capillary tube having an upstream tube portion, a tube bend portion, and a downstream tube portion, the downstream portion being substantially parallel to the upstream portion. A distance between the upstream tube portion and the downstream tube portion in one embodiment is no greater than half the upstream portion and downstream portion lengths, a first pair of thermal sensing elements are coupled to the upstream tube portion and a second pair of thermal sensing elements are coupled to the downstream tube portion.